High circulating vasopressin (VP) levels occur in man during cardiopulmonary resuscitation. The vasoconstrictor and antidiuretic of VP may be harmful to patients in certain clinical settings, e.g., coronary insufficiency and renal diseases. Clinical use of VP has been followed by myocardial infarction and deaths, and a cause and effect relationship has been implicated. However, adequate quantitation of Vp levels under many of these circumstances has not yet been obtained. The study of the pathophysiology of VP relies on an efficient, specific and sensitive method of measuremment. The most sensitive and widely used rat bioassay presents multiple technical difficulties. Radioimmunoassay fulfills the above requirements for the study of VP. High affinity rabbit anti-VP antibodies have been induced by hyper-immunization with VP or VP linked to a carrier protein. The antibodies have been used to establish a radioimmunoassay capable of detecting l pg (O.29 uU) of VP. The radioimmunoassay will be re-established in a new laboratory, and will be used to quantitate VP levels in man during cardiopulmonary resuscitation, general anesthesia and the post-operative period. Inhibition of VP release by various sedatives and tranquilizers will be evaluated in animals and in man. In addition, the specificity of the high affinity anti-VP antibodies with limited association constant heterogeneity will be characterized in detail.